DESCRIPTION: (Applicant's Abstract) The purposes of this study are to identify temporal trends and risk factors for new HIV infection in injecting drug users who are currently HIV negative but remain at high risk. This will be done by following a cohort of 1,000 HIV negative drug users at six month intervals for 3 years. This study will allow the evaluation of the factors associated with behavior change over time in this high risk population. It will also allow an evaluation of the field effectiveness of such interventions as drug treatment, needle exchange, needle disinfection and educational programs to reduce high risk behavior in order to prevent HIV infection in a population of drug users in Baltimore, who currently have a 4% annual incidence of HIV infection. In addition, morbidity and mortality rates in this population will be assessed and compared with an HIV-positive population being followed in the same clinic. This will allow evaluation of which illnesses in this population are HIV-related. The interaction between HIV and other common infections in this cohort, such as hepatitis B and C, tuberculosis, HTLV-II and pneumococci will be evaluated. This study will allow the identification of HIV seroconverters soon after they become infected. Detailed virological and immunological studies among recent HIV seroconverters will allow a better understanding of the early natural history of HIV infections in this population, in order to design intervention strategies to prevent rapid progression to AIDS. The proportion of AIDS cases in the United States among drug users and their children and sexual contacts is increasing. Control of the AIDS epidemic in the United States requires a better understanding of the current incidence and risk factors for HIV infection in this critical population.